Aliphatic polyamides, such as nylon 6 and nylon 66, and aromatic polyamides, such as poly-p-phenylene terephthalamide, are very useful polyamides and are produced on a commercial scale.
The former aliphatic polyamides are generally advantageous with respect to the case of handling and general purpose properties because they can be melt-polymerized and melt-shaped into shaped articles, such as fibers, films and molded articles. Aliphatic polyamides, such as nylon 66, however, have poor dimensional stability, even though they are widely used as tire cord materials in view of their high strength. Thus, it has been desired to improve the aliphatic polyamide so as to provide higher stiffness.
On the other hand, the latter aromatic polyamides, such as poly-p-phenylene terephthalamide and poly (1,4-benzamide), have excellent mechanical properties, such as high stiffness, because they contain an aromatic ring of rigid structure. These aromatic polyamides, however, cannot be melt-polymerized and melt-shaped. This leads to complexity in the method of production thereof and an increase in production costs. Thus, they are seriously inferior in general purpose properties compared to the foregoing aliphatic polyamides.
In addition, aromatic ring-containing polyamides, such as polyhexamethylene terephthalamide (nylon 6T), poly-p-phenylene adipamide (nylon P6) and a polyamide comprising piperazine and terephthalic acid, are known. These aromatic ring-containing polyamides, however, cannot be melt-polymerized and melt-shaped because of their high melting points. Thus, they suffer from the same problems as described for the foregoing aromatic polyamides.
Moreover, as melt-shapable aromatic ring-containing polyamides, polyhexamethylene isophthalamide (Nylon 6I), poly-m-xylylene adipamide (MXD-6), etc., are also known. These polyamides, however, do not have high stiffness.
Even in the case of copolymers which have been proposed to eliminate the foregoing drawbacks, for example, the copolymer as described in British Pat. No. 1,176,346 which is prepared by copolymerizing nylon 66 and nylon 6T, sufficient stiffness can not be obtained. These copolymers, therefore, are not improved to the extent that they are completely satisfactory for practical use.
Furthermore, aliphatic-aromatic polyamides having a high aromatic amide unit content have been proposed (for example, as described in Japanese Pat. No. 6733/1980). These aliphatic-aromatic polyamides, however, cannot be melt-polymerized or melt-shaped because of their high melting points.